The present invention relates to a method for preparing the windings for an electric motor, whereby the magnetic core of the stator and/or rotor of the electric motor are provided with slots in which winding coils can be fitted.
In electric motors, the windings are attached either directly to the stator and/or rotor or to the ferromagnetic part of the stator/rotor. In the latter case, the windings are fitted in slots machined in a laminated core of magnetic material or around separate pole shoes protruding from the stator/rotor frame. The present invention relates to the preparation of the windings for motors in which the windings are fitted in slots. More particularly, the invention concerns a motor having open slots.
In the stators of smaller alternating-current motors, a semi-closed slot is used in which widened tooth edges at the slot opening partially cover the slot, preventing the windings from moving. The design of the tooth edge can also be used to modify the properties of the motor, such as stray reactance and control of the magnetic flux in the air gap. However, due to the semi-closed slot, the winding operation is very laborious because the winding coils have to be inserted trough the narrow slot opening one wire or a few wires at a time. It is therefore difficult to keep the winding coil in shape and the coil needs shaping after the winding operation.
In motors with an axial air gap, the tooth width is small on the inner side of the motor and the space left over for the winding overhang is very limited. The coils have to be so shaped that they can be accommodated in the space reserved for them and that their insulation will not be damaged when the coils are being mounted in place. Preparing the windings requires several operations, which are automated and simplified as far as possible.
The object of the present invention is to develop a new procedure for preparing the windings for an electric motor, designed to eliminate the drawbacks described above and applicable especially in the case of windings mounted in open slots. In particular, the object is to create a procedure that is applicable for the preparation of windings for a motor with an axial air gap. To achieve this, the winding coils are wound from winding wire, the winding coils are shaped into a substantially final form, the winding coils are fitted in place in slots provided in a magnetic core. By winding the winding coils in a mould having a width substantially equal to the width of the motor slot, the coil side will already have its final shape, ready to be fitted in the slot. According to another embodiment, the coil does not have a cross-section exactly corresponding to the slot after the winding operation, but the cross-section of the coil sides is shaped e.g. by forcing them into formers shaped like the slots, by means of which the winding coils are twisted into their final shape.
According to an embodiment, the first coil side of a winding coil is fitted into one motor slot and the coil is turned so that the other coil side goes into another motor slot. The first coil side of each winding coil will thus go into the lower part of a slot, and a coil side of another coil will be placed on top of it, and the second coil side of the coil will go into the upper part of another slot on top of a third coil side in the case of a two-layer winding.
According to a preferred embodiment of the invention, the end windings have been formed into their final shape before the coil is fitted in the slots. This makes it unnecessary to turn the end windings while the coil is being mounted, and the end windings have been so bent that they will smoothly interlace with other end windings.
According to a preferred embodiment, each winding coil is a separate coil when it is being fitted into the slot, and after they have been fitted into the slots, the winding coils are connected together to form the desired winding. The winding coils are easy to produce as separate coils and they can be shaped and fitted into the slots faster than interconnected coils. The insulation is not so susceptible to being damaged. This procedure is particularly applicable to axial motors, in which the space for the winding overhang on the inner circle is very narrow.
According to an embodiment alternative to the previous one, two or more winding coils are connected in series before the coils are fitted into the slots, and the extreme wire ends of the series-connected coils are connected to other series of coils so as to form the desired winding. This will reduce, and in extreme cases eliminate, the work of soldering the windings together. This embodiment is applicable in the case of motors with sufficient space for the windings or in which the end windings are of the same shape at both ends of the slot, e.g. in linear motor applications.
After the winding coils have been fitted into the slots, the slots are preferably closed with ferromagnetic wedges inserted into chases formed in the slots. The coils rest against the wedges in the depth direction of the slot and no special measures are needed after the wedge has been mounted. The use of slot wedges also results in an air gap flux free of harmonics, so the vibrations and noise caused by harmonics is substantially reduced. This is a significant feature especially in a synchronous motor with permanent magnets because the number of stator slots is normally divisible by the number of magnets on the rotor. All the magnets are therefore in the same position with respect to stator slots. Thus, changes in flux density in the symmetrically divided air gap at the edges of the slot openings/teeth produce axial and tangential forces in all magnets at the same time and in the same direction. By shaping the slot wedge, it is possible to influence the flux control and therefore also the vibration and noise level as well as stray reactances in the motor. In this way it is also possible to achieve magnetic properties in the air gap surface of the motor that are nearly equivalent to those of a semi-closed slot.
In the case of an axial or conical motor, the slots at the edge closer to the axis are closer to each other than at the outer edge. In this case, the coils are preferably so shaped already during the winding operation that the end windings differ in length, by making the first end winding, which lies closer to the axis, shorter than the second end winding, which is farther removed from the axis.
Further preferred embodiments are defined in the subclaims.